It is well known to provide a refrigerating apparatus with a plurality of evaporators for individually refrigerating a plurality of refrigerating chambers. The temperature in each refrigerating chamber is controlled by operation of electromagnetic valves, each of which is serially connected with a respective evaporator to control the flow of refrigerant through each evaporator.
FIG. 1 shows a known refrigerating apparatus. The refrigerating apparatus includes compressor 1, oil separator 2, condenser 3, a plurality of evaporators 6, a plurality of electromagnetic valves 4, a plurality of capillary tubes 5, and accumulator 7. These elements are coupled in series to form a closed refrigerating circuit. That is, each respective electromagnetic valve 4, capillary tube 5, and evaporator 6 are connected in series, and the resulting electromagnetic valve-capillary tube-evaporator combinations are coupled in parallel. These parallel combinations are connected in series with compressor 1 and condenser 3 through distributor 8. Electromagnetic valves 4 control refrigerant flow and capillary tubes 5 function as expansion valves or decompression devices. Thus, if the operation of each electromagnetic valve 4 is controlled by the signal from a respective temperature detecting device disposed on each refrigerating chamber, the temperature in each refrigerating chamber can be maintained at a predetermined level.
In the above refrigerating circuit, the capacity of the compressor should be chosen to supply refrigerant to all evaporators to properly operate each evaporator. The temperature in each chamber is individually controlled by the operation of its electromagnetic valve, and each chamber is normally maintained at a different temperature than the others. Therefore, sometimes many or most of the electromagnetic valves are closed at the same time. During these instances, the capacity of the compressor exceeds the required capacity of the refrigerating apparatus. If the capacity of the compressor exceeds the required capacity for the refrigerating apparatus, the pressure in the suction port side of the compressor is reduced and vacuum conditions are reached. However, when the compressor is driven under vacuum conditions, atmospheric air can easily enter into the refrigerating circuit. The atmospheric air contains moisture, this moisture freezes on the capillary tube, and the flow of refrigerant is obstructed.
To resolve these disadvantages, a pressure switch is disposed on the suction port side of the compressor. The operation of the compressor ceases when the suction pressure falls below the predetermined pressure which is detected by the pressure switch. However, if the compressor is provided with a pressure switch, the compressor is intermittently driven by the temperature change in the chambers, as well as by the suction pressure change. This decreases the durability of the compressor, and the temperature in the chambers is not stabilized.